This research proposal is designed to study how the mother and her environment act to coordinate the phase of developing circadian periodicity in the fetal and noenatal rat. Pineal melatonin production will be used to monitor circadian output from the suprachiasmatic nuclei (SCN; a biological clock) in the developing rat during the first 3 weeks of life. Either wheel-running activity or burrow emergence behavior will be used to monitor circadian function in the mother and in older pups. The first series of experiments will focus on the factors which influence the phase of circadian periodicity in the fetal SCN. It will be established whether the fetus can perceive alterations in environmental lighting or whether this information is transduced by mother and then communicated to the fetus. Next, the effects of ablation of the SCN and pinealectomy in the mother on her ability to transduce circadian information to the fetus will be studied. The second set of experiments will focus on the factors which influence circadian periodicity in the postnatal period. First, the ability of retinal and extraretinal photoreception to coordinate the phase of circadian periodicity in the postnatal animal will be examined. Experiments will then be directed at study of the maternal influence on the phase of developing circadian periodicity in the postnatal period which will be examined using blinded pups housed in conventional cages and intact pups maintained in an artificial burrow environment. These conditions are designed to stimulate a natural environment in which maternal communication of information about lighting to pups can be studied. This will allow for an examination of the effects of ablation of the SCN and pinealectomy in mother on her ability to communicate lighting information to her pups. Finally, it will be determined whether maternal coordination confers an adaptive advantage to the pups at the time of emergence from the burrow into the environment.